A review on mechanism, quality preservation and energy efficiency in Refractance Window drying: a conductive hydro-drying technique

Thermal drying consumes up to 25% of the industrial energy consumption in developed countries. Refractance Window (RW) is a relatively new drying method that it is characterized by maintaining a relatively low temperature inside the food and short drying times. A RW dryer uses circulating hot water as a means to convey thermal energy to materials to be dehydrated. A RW dryer can produce high-quality products with retaining heat sensitive vitamins, co­­­­lor, phytochemicals content and antioxidant activity close to the freeze-dried products, while the cost of the RW equipment is less than 30 percent of the cost of a freeze-dryer and the energy consumption of RW is less than 50 percent of the energy consumption for a freeze-dryer. Early understandings heat transfer mechanism in RW drying suggested that the moist material on a thin plastic sheet over hot water, creates a “window” for infrared radiation(IR) and as the material dries, the “window” gradually cuts off the radiation. Recently a conjugate heat and mass transfer model showed that a major portion of thermal energy is transferred via conduction; some of the researchers proposed the term “conductive hydro-drying” for the name of this technology. Another important parameter in RW drying is air convection. Forced air convection causes lower product temperature and higher moisture loss in comparison with natural convection. Although many studies have been conducted on this technology, there are still many types of food materials for which RW drying and process optimization have not yet been investigated

An Update on Applications of Power Ultrasound in Drying Food: A Review

Ultrasound is sound waves with above the human hearing range frequency that is approximately 20 kHz. Application of power ultrasound in combination with other food processing methods including drying, is considered to be an emerging and promising technology. The use of novel non-thermal technologies, such as power ultrasound, is suitable to facilitate the drying of heat sensitive food materials. Ultrasound enhance heat and mas transfer which result in faster moisture removal during drying due to heating, vibration and synergistic effects. These effects could lead to product quality preservation in terms of color, texture, vitamin C and antioxidants content, by the use of milder drying conditions, and in some cases can promote better energy efficiency. In this article, after a brief review on the history of ultrasonic drying, different methods are categorized and combinations of ultrasound with novel drying methods and their effects on phytochemicals are discussed with the focus on the recently published articles. Studies showed that the quality of ultrasonically dried products was usually higher than conventionally dried products. However, the effect of ultrasonic drying on the texture and nutritional value of the products should be further investigated

Influence of Persian gum and almond gum on the physicochemical properties of wheat starch

In this study, the influence of different levels (0.1, 0.2, and 0.3% w/w) of Persian gum or almond gum were incorporated into wheat starch, and their influences on water absorption, freeze–thaw stability, microstructure, pasting, and textural properties were investigated. The SEM micrographs revealed that the addition of hydrocolloids to starch leads to the formation of denser gels with smaller pores. The water absorption of starch pastes was improved in the presence of gums, and samples containing 0.3% almond gum had the highest water absorption. The rapid visco analyzer (RVA) data showed that the incorporation of gums significantly affected the pasting properties by increasing the pasting time, pasting temperature, peak viscosity, final viscosity, and setback and decreasing breakdown. In all the pasting parameters, the changes caused by almond gum were more obvious. Based on TPA measurements, hydrocolloids were able to improve the textural properties of starch gels, such as firmness and gumminess but decreased the cohesiveness, and springiness was not affected by the incorporation of gums. Moreover, the freeze–thaw stability of starch was enhanced by the inclusion of gums, and almond gum exhibited better performance

Shelf life of unpasteurized sour orange juice in Iran

Introduction. In Iran, sour orange is available between mid-October and March. Frequently, consumers store a large volume of unpasteurized juice at room or low temperatures for consumption when the fresh fruit is not available. The aim of our research was to determine the shelf life of unpasteurized sour orange juice which was stored under conditions similar to those adopted by consumers at home. Materials and methods. Sour orange juice was prepared by hand-squeezing fresh fruit; it was filtered, and then poured into clear or dark green glass bottles. Bottles were stored at room temperature [(28 ± 2) °C], in the refrigerator [(4 ± 1) °C] and in the freezer [(–12 ± 1) °C] for 12 weeks. Additional samples were prepared by supplementing juice with 2% (w/w) citric acid and they were stored in the refrigerator. Total soluble solids and pH values were measured every 2 weeks and analysis was carried out on ascorbic acid content by means of the titration method in the presence of 2,6–dichlorophenol indophenol. The study was performed for 12 weeks. Results and discussion. Total soluble solids content and pH value of the initial juice were 11.5 °Brix and 3.18, respectively. pH appeared not to be significantly influenced by storage time or conditions; however, total soluble solids content in a few samples was reduced to about 9.5 °Brix. The initial ascorbic acid content was 130 mg·100 mL–1; after 2 weeks, it was reduced by nearly 50% for all unfrozen samples. The final concentration of ascorbic acid in the juice was approximately 20 mg·100 mL–1, regardless of storage conditions. The deteriorative reaction of ascorbic acid in the juice at each temperature experienced followed a first-order kinetic model with activation energy of 2.67 kJ·mol–1

Ohmic hydrodistillation, an accelerated energy-saver green process in the extraction of Pulicaria undulata essential oil

Ohmic-assisted hydrodistillation (OAHD) is a promising extraction process in which the internal heating and electroporation phenomenon occur owing to electrical current passing through the plant materials. Extraction time, yield, and properties of Pulicaria undulata essential oils obtained through OAHD was investigated and compared to conventional hydrodistillation (HD). Time required to complete the extraction was considerably shorter in OAHD (61 min) with significantly higher yield (1.50%), compared to HD (159 min and 1.34%). A comparable chemical profile of essential oils was obtained with higher percentage of 1,8-cineole (14.68%) and chrysanthenone (10.25%) in OAHD than HD. The investigated essential oils also exhibited antibacterial and antioxidant activity with OAHD essential oil being more effective. The electrical energy consumption for OAHD was almost half of that measured for HD. In this regard and on the basis of equivalent CO2 emission, OAHD may well be categorized as a "green extraction technology". (C) 2017 Elsevier B.V. All rights reserved

Impact of ohmic-assisted hydrodistillation on kinetics data, physicochemical and biological properties of Prangos ferulacea Lindle. essential oil: comparison with conventional hydrodistillation

The effect of ohmic-assisted hydrodistillation (OAHD) as an emerging technology, on the extraction kinetics and characteristics of the Prangos ferulacea Lindle. essential oil was studied, and the results were compared to hydrodistillation (HD). According to the results, to achieve a similar yield OAHD required half the time required by the HD. GC/MS results indicated considerable differences in the quantity of the main components, and selective extraction of limonene and (E)-beta-ocimene was obtained through OAHD (13.32% and 23.60%, respectively). This could be attributed to the rapid increase in temperature as a result of internal heating and electroporation occurrence due to electrical current passing through the material. The Prangos ferulacea essential oils exhibited antibacterial and antioxidant activities. The electrical energy consumption for the OAHD was almost one half of that consumed by the conventional HD extraction. Based on equivalent CO2 emission, OAHD may be considered as a "novel green technology".Industrial relevance: Application of emerging thermal technologies such as ohmic heating has been introduced to essential oil extraction and presented some desirable advantages over the conventional methods, such as effective heating, fast energy transfer, time saving and low operating costs, and no adverse alterations in chemical compositions. In this study, ohmic-assisted hydrodistillation was used to extract the essential oils of Prangos ferulacea. The results of this study showed that not only a selective extraction of some components can achieve via ohmic procedure, but also it is a more economical and environmentally friendly procedure that can be considered as a green technology. (C) 2015 Elsevier Ltd. All rights reserved

Effects of ultrasound and infrared assisted conductive hydro-drying, freeze-drying and oven drying on physicochemical properties of okra slices

Okra (Abelmoschus esculentus) is a nutritious vegetable but it is highly perishable and drying is one of the best methods for its preservation. Ultrasound and infrared assisted conductive hydro-drying (UIACHD) is a new patented drying method that can dry food materials with high quality and high energy efficiency. In this study, okra slices were dried using UIACHD with different settings and also by freeze-drying and oven drying. The UIACHD drying curves, moisture content, color, vitamin C content, hydrocolloids rheology and microstructure of the dried okra sample as affected by drying method were investigated. Drying curves showed that the application of ultrasound and infrared could increase the drying rate. In terms of quality parameters, UIACHD performed significantly better than oven drying and the quality of the products was comparable to freeze-drying. Flow and oscillation rheology tests showed that UIACHD drying could result in okra hydrocolloids with higher apparent viscosity and the application of ultrasound and infrared has preserved the rheological properties of the okra hydrocolloids. The microstructure of the dried okra slices was also well preserved by UIACHD. This study showed that UIACHD is a suitable drying method for maintaining the physicochemical quality of dried okra

Ultrasound pretreatment impact on Prangos ferulacea Lindl. and Satureja macrosiphonia Bornm. essential oil extraction and comparing their physicochemical and biological properties

The aim of this study was to investigate the impact of ultrasonic pretreatment (US + HD) of Prangos ferulacea Lindl. and Satureja macrosiphonia Bornm. leaves prior to hydrodistillation (HD). The two plants differed in their secretory structures, internal and external structures, respectively. Extraction kinetics, chemical composition, physical and biological properties of the essential oils was evaluated. Although applying ultrasound pretreatment resulted in a faster extraction process, no significant difference was observed between the yields. Similar main components in essential oils including p-cymene, limonene, (E)-beta-ocimene, terpinolene, and 2,3,6-trimethylbenzaldehyde for P. ferulacea and cis-sabinene hydrate, linalool, borneol, and terpinene-4-ol for S. macrosiphonia were observed, regardless of applying sonication or not. However, a selective extraction of limonene (P. ferulacea) and linalool (S. macrosiphonia) was a direct result of 15 min indirect sonicatin of plant materials prior to hydrodistillation. Ultrasonic pretreatment not only had no adverse effect on biological properties of extracted essential oils but also in case of pre-treated P. ferulacea improved antioxidant activity. Generally, this study indicates that ultrasonic pretreatment of plant materials resulted in accelerating the essential oil extraction process and producing an essential oil with superior characteristics. (C) 2016 Elsevier B.V. All rights reserved

Combined ultrasound and infrared assisted conductive hydro-drying of apple slices

Conductive hydro-drying also known as Refractance Window drying is a relatively new drying technology, which uses hot water to carry thermal energy to materials to be dehydrated. It has a high retention of heat sensitive quality parameters (vitamins, antioxidants, and color) with better energy efficiency than freeze-drying as well as many other conventional drying methods. A new ultrasound and infrared assisted conductive hydro-dryer (UIACHD) was developed to increase drying rate while reducing required hot water temperature and increasing the drying material thickness. The goal of this study was to evaluate the performance of the new dryer and to compare the performance of a pilot scale continuous UIACHD with a freeze-dryer and a cabinet dryer in drying apple slices. The physiochemical characteristics of the dried apple slices including flavonoid content, total phenolic compounds, antioxidant activity, vitamin C content and color were measured. In addition, the energy consumption and energy efficiency of the dying methods were evaluated. Results showed that combining ultrasound and infrared with conductive hydro-drying can result in higher drying rates and lower product moisture content. Quality of UIACHD dried apple slices was close to the freeze-dried products and it was significantly better than the cabinet dried products. Moreover, the energy efficiency of UIACHD was considerably better than the cabinet dryer and the freeze-dryer. The results of this study showed that combining ultrasound and infrared with conductive hydro-drying can lead to an energy-efficient process with good quality retention ability

Efficiency of Tragacanth gum coating enriched with two different essential oils for deceleration of enzymatic browning and senescence of button mushroom (Agaricus bisporus)

The effect of Tragacanth gum (T) coating containing (100, 500, and 1,000 mg/L) Satureja khuzistanica essential oil (S), Zataria multiflora Boiss. essential oil (Z), and (1,000 mg/L) sodium metabisulfite (M) on mushroom (Agaricus bisporus) enzymatic browning and postharvest quality was examined throughout 16 days of cold storage. Mushroom respiration rate, soluble solids content (SSC), percentage of open caps, and sensory quality as well as factors related to browning such polyphenol oxidase (PPO), phenylalanine ammonia lyase (PAL), and peroxidase (POD) activities were figured out. The significant decrease in respiration rate, cap opening delay, and SSC enhancement was observed after treating mushrooms with TZ and TS. Moreover, TZ‐ and TS‐treated mushrooms prevented enzymatic browning through inhibiting PPO and POD activities and increasing activity of PAL over the storing term. Additionally, the influence of TZ5 and TS5 (containing 500 mg/L essential oil) coatings was validated by sensory evaluation through protecting the overall quality of button mushrooms over the storage. Thus, Tragacanth coating enriched with essential oils might be an encouraging nomination for improving the modality of button mushroom and expanding its shelf life